Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0021051 (immunodeficiency)
 71,517 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The structural requirements for proteolytic cleavage of the human immunodeficiency virus type 1 env gene product, gp160, to gp120 and gp41 have been assessed by specific mutagenesis of the sequence Lys Ala Lys Arg Arg Val Val Glu Arg Glu Lys Arg located between amino acids 500 and 511, i.e., at the putative C terminus of gp120. The basic amino acids underlined have been mutated, individually and in combination, to neutral amino acids, and the cleavability of the mutated env gene products was examined after expression in CV-1 cells. The results show that the replacement of Arg-511 (cleavage presumably occurs C terminal to this amino acid) with Ser completely abolishes recognition and cleavage by the cellular protease(s), i.e., the remaining basic amino acids in the vicinity do not serve as alternative substrates. However, Arg-508 and Lys-510 are important features of the recognition site since, when they are individually changed to neutral amino acids, cleavage is severely impaired. The basic amino acids 500, 502, and 504 are, individually, not important for cleavage, since their individual replacement by neutral amino acids does not impair cleavage. However, when all four basic amino acids 500, 502, 503, and 504 are changed to neutral amino acids, cleavage is almost completely abolished. This shows that the sequence Arg Glu Lys Arg at the cleavage site is alone not sufficient for cleavage but that a contribution of other amino acids is required, whether the other amino acids provide a basic character or a certain structure in the vicinity of the cleavage site. When noncleavable or poorly cleavable mutant env genes are expressed from the infectious plasmid pNL4-3 in CD4+ human lymphoblastoid cells, noninfectious virus, incapable of spread throughout the culture, is produced.
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PMID:Mutational analysis of the human immunodeficiency virus type 1 env gene product proteolytic cleavage site. 218 11

A synthetic DNA fragment encoding a protease precursor of the human immunodeficiency virus type 2 (HIV2) was cloned and expressed in bacteria and yeast. A recombinant plasmid encoding a hybrid polypeptide consisting of human superoxide dismutase and an HIV2 protease precursor of 113 amino acids was constructed for regulated intracellular expression in bacteria. Induction of this plasmid produced an autoprocessed form of the retroviral enzyme possessing the correct molecular weight. Overexpression and secretion of the protease from yeast was achieved with an expression vector encoding the yeast pheromone alpha-factor signal/leader sequence fused to a protease precursor of 115 amino acids. Amino-terminal sequence analysis confirmed that the viral enzyme exported from yeast was correctly processed from its precursor by cleavage of the predicted Ala-Pro peptide bond located at the NH2 terminus of the protease in the pol open reading frame. No additional amino acid residues were required at the COOH terminus of the protease for this autoproteolytic event. The HIV2 protease expressed in bacteria and yeast was active in an in vitro assay when tested on the HIV1 polyprotein precursor, myristylated Pr53gag. Two synthetic peptides representing junction sequences in the HIV1 gag-pol precursor were used to assay purified HIV2 protease. The enzyme exhibited a kcat/KM of 23.2 min-1 mM-1 on the HIV1 matrix-capsid junction peptide and a kcat/KM of 71.4 min-1 mM-1 on the protease-reverse transcriptase junction peptide. These rates show that the HIV2 enzyme is efficient at hydrolyzing the HIV1 peptide junctions, revealing the analogous nature of the substrate specificities of the two enzymes.
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PMID:Recombinant HIV2 protease processes HIV1 Pr53gag and analogous junction peptides in vitro. 219 46

Highly purified, recombinant preparations of the virally encoded proteases from human immunodeficiency viruses (HIV) 1 and 2 have been compared relative to 1) their specificities toward non-viral protein and synthetic peptide substrates, and 2) their inhibition by several P1-P1' pseudodipeptidyl-modified substrate analogs. Hydrolysis of the Leu-Leu and Leu-Ala bonds in the Pseudomonas exotoxin derivative, Lys-PE40, is qualitatively the same for HIV-2 protease as published earlier for the HIV-1 enzyme (Tomasselli, A. G., Hui, J. O., Sawyer, T. K., Staples, D. J., FitzGerald, D. J., Chaudhary, V. K., Pastan, I., and Heinrikson, R. L. (1990) J. Biol. Chem. 265, 408-413). However, the rates of cleavage at these two sites are reversed for the HIV-2 protease which prefers the Leu-Ala bond. The kinetics of hydrolysis of this protein substrate by both enzymes are mirrored by those obtained from cleavage of model peptides. Hydrolysis by the two proteases of other synthetic peptides modeled after processing sites in HIV-1 and HIV-2 gag polyproteins and selected analogs thereof demonstrated differences, as well as similarities, in selectivity. For example, while the two proteases were nearly identical in their rates of cleavage of the Tyr-Pro bond in the HIV-1 gag fragment, Val-Ser-Gln-Asn-Tyr-Pro-Ile-Val, the HIV-1 protease showed a 64-fold enhancement over the HIV-2 enzyme in hydrolysis of a Tyr-Val bond in the same template. Accordingly, the HIV-2 protease appears to have a different specificity than the HIV-1 enzyme; it is better able to hydrolyze substrates with small amino acids in P1 and P1', but is variable in its rate of hydrolysis of peptides with bulky substituents in these positions. In addition to these comparisons of the two proteases with respect to substrate specificity, we present inhibitor structure-activity data for the HIV-2 protease. Relative to P1-P1' statine or Phe psi [CH2N]Pro-modified pseudopeptidyl inhibitors, compounds having Xaa psi[CH(OH)CH2]Yaa inserts were found to show significantly higher affinities to both enzymes, generally binding from 10 to 100 times stronger to HIV-1 protease than to the HIV-2 enzyme. Molecular modeling comparisons based upon the sequence homology of the two enzymes and x-ray crystal structures of HIV-1 protease suggest that most of the nonconservative amino acid replacements occur in regions well outside the catalytic cleft, while only subtle structural differences exist within the active site.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Specificity and inhibition of proteases from human immunodeficiency viruses 1 and 2. 220 91

Acquired immunodeficiency syndrome (AIDS) is initiated by the attachment of the human immunodeficiency virus (HIV) to a surface glycoprotein CD4 present on T4 helper/inducer lymphocytes, monocytes/macrophages and other cells. A simple octapeptide (H-Ala-Ser-Thr-Thr-Thr-Asn-Tyr-Thr-OH, peptide T) seems to inhibit HIV infectivity and to activate human monocyte chemotaxis. In order to study in vitro metabolic stability and structure-activity relationships, peptide T and a number of analogues were prepared and tested on human monocytes by chemotactic assay. Peptide T and the shorter fragments T(3-8)-OH and T(4-8)-OH displayed potent bioactivity (maximal chemotactic activity in the range 10(-11)-10(-10) M). The C-terminal heptapeptide showed a reduction of potency, while further truncations at N-terminus of T(4-8)-OH abolished the biological action. In the octapeptide series, whereas the alpha-amino butyric acid (Abu) substitution for Thr4 was well tolerated, the same "slight" structural change at Thr5 or Thr8 was very detrimental. Finally, [D-Asn6]T(1-8)-OH analogue has low chemotactic activity. All these results indicate that i) the C-terminal pentapeptide is the minimum sequence required for bioactivity, ii) residues 5 to 8 appear to play a crucial biological role, iii) peptide T chemotaxis is mediated, at least in part, through the polar properties of Thr side chains at the critical positions 5 and 8, while the Thr4 does not interfere with biological characteristics of peptides.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Synthesis, metabolic stability and chemotactic activity of peptide T and its analogues. 232 89

We previously reported the in vitro generation of a neutralization-resistant variant of the molecularly cloned isolate of human immunodeficiency virus type 1 (HIV-1), HXB2D. The molecular basis for the resistance was shown to be a point mutation in the env gene, causing the substitution of threonine for alanine at position 582 of gp41. Here, we show the variant to be resistant to syncytium inhibition as well as to neutralization by the immune-selecting serum. Moreover, 30% of HIV-positive human sera able to neutralize the parental virus have significantly decreased ability to neutralize the variant. As the A-to-T substitution thus has general relevance to the interaction of HIV-1 with the host immune system, we investigated further the biologic and immunologic bases for the altered properties. Synthetic peptides corresponding to the 582 region failed to compete in infectivity, neutralization, or syncytium inhibition assays and did not elicit neutralizing antibodies. Furthermore, human antibodies, affinity purified on synthetic peptide resins, bound to gp41 and peptides from the 582 region but did not possess neutralizing antibody activity. Some viral constructs in which the AVERY sequence in the 582 region was altered by site-directed mutagenesis were not infectious, indicating that the primary structure in this region is crucial for viral infectivity. Constructs predicted to possess a local secondary structure similar to that of the variant nevertheless behaved like the parental virus and remained neutralization sensitive. These results suggest that the requirements for neutralization resistance in this region are very precise. Our results with synthetic peptides show that the 582 region does not by itself constitute a neutralization epitope. Moreover, the degree of flexibility in amino acid substitution which allows maintenance of neutralization sensitivity suggests that position 582 does not form part of a noncontiguous neutralization epitope. The basis for neutralization resistance of the immune-selected variant is more likely a conformational change altering a neutralization epitope at a distant site.
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PMID:The site of an immune-selected point mutation in the transmembrane protein of human immunodeficiency virus type 1 does not constitute the neutralization epitope. 235 23

Infection of mononuclear cells by human immunodeficiency virus (HIV) begins with binding of the viral envelope glycoprotein, gp120, to its receptor, CD4. CD4 contains four extracellular immunoglobulin-like domains, the first of which (V1) is sufficient for HIV binding. V1 contains three sequences homologous to the antigen-complementarity-determining regions (CDR1 to -3) of immunoglobulin variable domains. While all three immunoglobulin CDRs are involved in antigen binding, only amino acids within and flanking the CDR2-like region of CD4 have been shown previously to be involved in gp120 binding. To investigate whether other regions in V1 take part in gp120 binding, we substituted alanine for each of 64 amino acids, including all of the hydrophilic residues in this domain. Mutations at four locations outside the CDR2-like sequence (amino acids 29, 59-64, 77-81, and 85) markedly affected gp120 binding, but not the overall structure of V1 as probed with eight conformationally sensitive monoclonal antibodies. Thus, the gp120-binding site of CD4 is not limited to the CDR2-like sequence and consists of several discontinuous segments. Several amino acids were identified that are critical for the conformation of V1; the importance of these residues suggests some differences in the folding of this domain compared to immunoglobulin variable domains. Three amino acid substitutions were found that increase the affinity for gp120 significantly (1.7- to 2-fold individually and 4.2-fold when combined), suggesting that it may be possible to improve the HIV-blocking ability of CD4-based molecules by increasing their gp120 binding affinity.
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PMID:Mapping the CD4 binding site for human immunodeficiency virus by alanine-scanning mutagenesis. 240 98

Covalent linkage of myristic acid to the N-terminal glycine residue of Pr55gag, the precursor of the major structural proteins of human immunodeficiency virus 1 (HIV-1), facilitates an essential step in virus assembly and propagation. Substitution of the myristoyl-acceptor glycine with alanine, in a functional clone of HIV-1, eliminates virus replication. Complementation of this defect, in trans, restores infectious particle production. The nonmyristoylated (myr-) gag precursor accumulates in infected cells and is not processed into the mature capsid components of the intact virion. However, myr- Pr55gag can be processed by purified HIV protease in vitro, demonstrating that the myristoyl moiety is not required for cleavage by the protease. Myristoylation of Pr55gag is not necessary for localization but is required for stable membrane association and assembly of HIV-1.
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PMID:Myristoylation-dependent replication and assembly of human immunodeficiency virus 1. 240 82

A highly immunogenic epitope from a conserved COOH-terminal region of the human immunodeficiency virus (HIV) gp120 envelope protein has been identified with antisera from HIV-seropositive subjects and a synthetic peptide (SP-22) containing 15 amino acids from this region (Ala-Pro-Thr-Lys-Ala-Lys-Arg-Arg-Val-Val-Gln-Arg-Glu-Lys-Arg). Peptide SP-22 absorbed up to 100% of anti-gp120 antibody reactivity from select HIV+ patient sera in immunoblot assays and up to 79% of serum anti-gp120 antibody reactivity in competition RIA. In RIA, 45% of HIV-seropositive subjects had antibodies that bound to peptide SP-22. Human anti-SP-22 antibodies that bound to and were eluted from an SP-22 affinity column reacted with gp120 in RIA and immunoblot assays but did not neutralize HIV or inhibit HIV-induced syncytium formation in vitro, even though these antibodies comprised 70% of all anti-gp120 antibodies in the test serum. In contrast, the remaining 30% of SP-22 nonreactive anti-gp120 antibodies did not react with gp120 in immunoblot assays but did not react in RIA and neutralized HIV in vitro. Thus, approximately 50% of HIV-seropositive patients make high titers of nonneutralizing antibodies to an immunodominant antigen on gp120 defined by SP-22. Moreover, the COOH terminus of gp120 contains the major antigen or antigens identified by human anti-gp120 antibodies in immunoblot assays.
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PMID:A conserved region at the COOH terminus of human immunodeficiency virus gp120 envelope protein contains an immunodominant epitope. 243 31

To determine the influence of concurrent human immunodeficiency virus (HIV) infection on chronic hepatitis B virus (HBV) infection, 150 male homosexual chronic hepatitis B surface antigen (HBsAg) carriers were studied. Of these, 82 subjects (55%) tested positive for antibodies to HIV. They were more likely to express hepatitis B "e" antigen (HBeAg) (P less than .001) and HBV-DNA (P less than .0005) in serum than were HIV-seronegative individuals. However, the degree of immune suppression did not influence HBeAg-HBV-DNA expression. In HBeAg-seropositive subjects, concurrent HIV infection was associated with lower serum alanine transferase levels (P less than .001). This effect increased with the degree of immune suppression as determined by CD4+ lymphocyte counts. Conversely, in patients negative for HBeAg, there was a weak trend towards higher alanine transferase levels with concurrent HIV. This study suggests that chronic hepatitis B may be less severe when accompanied by HIV infection; however, greater viral replication may make it more contagious and resistant to antiviral therapy. These data support an immune-mediated pathogenesis for hepatitis B and have implications for its control.
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PMID:The effect of concurrent human immunodeficiency virus infection on chronic hepatitis B: a study of 150 homosexual men. 257 46

Conformational analysis, based on ECEPP (Empirical Conformational Energy Program for Peptides) using the chain build-up procedure, was applied to determine the low-energy conformations for a series of tetrapeptides. The tetrapeptides are components of larger peptides which have been found to bind to the CD4 receptor of monocytes. Several previous studies have implicated the tetrapeptide units investigated here as being critical to the biological activities of the full peptides. Five such tetrapeptides were studied: Ser-Ser-Asn-Tyr (from ribonuclease A), Thr-Thr-Asn-Tyr (from peptide T, known to block human immunodeficiency virus from attaching to CD4+ T cells), Thr-Ile-Asn-Tyr (from polio virus coat protein, which is less active than the other peptides in binding to CD4 receptors), Ser-Ser-Ala-Tyr (from the gp 120 coat protein of human immunodeficiency virus, a variant of the peptide T sequence, active in blocking viral attachment to CD4+ cells), and the tetrapeptide from an active synthetic pentapeptide, Asn-Thr-Lys-Tyr (from Asn-Thr-Lys-Tyr-Thr). Using a 7 kcal/mol cutoff, the low-energy conformations for each peptide were computed. Approximately 20,000 conformations were computed for each tetrapeptide. Residue probability profiles were determined for each tetrapeptide. All tetrapeptides except for the polio sequence showed flexibility in the sense that many low-energy conformations were possible. In previous studies, it was postulated that the critical tetrapeptide units would adopt conformations similar to the one observed in a segment of ribonuclease A, residues 22-25, a beta-bend, which is part of an octapeptide segment (residues 19-26) that is homologous to the sequence of peptide T.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Correlation of beta-bend conformations of tetrapeptides with their activities in CD4-receptor binding assays. 259 73


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